Photostable liquid-crystalline medium

Abstract

The invention relates to a photostable liquid-crystalline medium comprising at least one compound of the formula I  and at least one compound of the formula II  and to the use thereof for electro-optical purposes, and to displays containing this medium.

1. A liquid-crystalline medium comprising
 at least one compound of formula I 
 
       
         
           
           
               
               
           
         
          and 
         at least one compound of formula II 
       
       
         
           
           
               
               
           
         
          in which 
         L 1 , L 2 , L 3  and L 4  are each, independently of one another, H or F; 
         R 11  is H, a halogenated or unsubstituted alkyl radical having from 1 to 15 carbon atoms, where, in addition, one or more CH 2  groups in these radicals may each be replaced, independently of one another, by —C≡C—, —CH═CH—, —O—, —CO—O—or —O—CO— in such a way that O atoms are not linked directly to one another; 
         R 21  and R 22  are each, independently of one another, H, Cl, F, CN, SF 5 , SCN, NCS, a halogenated or unsubstituted alkyl radical having from 1 to 15 carbon atoms, where, in addition, one or more CH 2  groups in these radicals may each be replaced, independently of one another, by —C≡C—, —CH═CH—, —O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another; 
         Y 11  is F, Cl, CN, SF 5 , SCN, NCS, a halogenated alkyl radical, a halogenated alkenyl radical, a halogenated alkoxy radical or a halogenated alkenyloxy radical, each having up to 6 carbon atoms; 
         Z 11  is a single bond, 
         a, is 1; 
         b, c, d and e are each, independently of one another, 0, 1 or 2; 
         f is 1; 
       
       
         
           
           
               
               
           
         
       
     
     
       2. The liquid-crystalline medium according to  claim 1 , wherein the proportion of the compounds of the formula II in the mixture as a whole is from 0.1 to 10% by weight. 
     
     
       3. An electro-optical liquid-crystal display containing a liquid-crystalline medium according to  claim 1 . 
     
     
       4. The liquid-crystalline medium according to  claim 1  wherein the proportion of the compounds of formula II in the mixture as a whole is 0.25 to 5% by weight. 
     
     
       5. The liquid-crystalline medium according to  claim 1  wherein the proportion of the compounds of formula II in the mixture as a whole is 0.5 to 2% by weight. 
     
     
       6. The liquid crystalline medium according to  claim 1 , wherein the compound of formula I is 
       
         
           
           
               
               
           
         
       
     
     
       7. The liquid crystalline medium according to  claim 1 , wherein the compound of formula I is 
       
         
           
           
               
               
           
         
       
     
     
       8. The liquid crystalline medium according to  claim 1 , wherein the compound of formula I is 
       
         
           
           
               
               
           
         
       
     
     
       9. The liquid crystalline medium according to  claim 1 , wherein the compound of formula I is 
       
         
           
           
               
               
           
         
       
     
     
       10. The liquid crystalline medium according to  claim 1 , wherein the compound of formula II is